[clang] [PAuth] Use different discriminators for __int128_t / __uint128_t / _BitInt(n) (PR #140276)

[Oliver Hunt via cfe-commits]

ojhunt wrote:

@ahatanak I've discussed this with @asl in discord, I think this is a sensible change my only real concern is the ABI, even though it would in principle require the effected types being used in an ABI exposed way to matter

https://github.com/llvm/llvm-project/pull/140276